Controlled embossing



'l Feb; 11, 1969 f3.1; HOFFMAN 3,426,571

CONTROLLED EMBOSS ING Filed Jan. 27, 1967 Sheet of 5 Feb. l1, 1969 B. L.. HOFFMAN u 3,426,571 CONTROLLED EMBossING Filed Jan. 27, 1967 A sheet om Feb. 1l, 1969 5.1.. HOFFMAN 3,426,571

CONTROLLED EMBossING Filed Jan. 27, 1967 Sheet of ArrceP/vys United States Patent O 3,426,571 CONTROLLED EMBOSSING j Bernard L. Hoffman, Trenton, NJ., assignor to Frederick A. Krause Associates, Inc., Frenchtown, NJ., a corporation of New Jersey Filed Jan. 27, 1967, Ser. No. 612,185

U.S. Cl. 72-335 10 Claims Int. Cl. B21d 28/10, `37/10; B21j 13/04 ABSTRACT F THE DISCLOSURE Tear strip formation on sheet metal objects during press formation thereof by limiting the minimum clearance between die shoes and absorbing excess motion by allowing the die shoes to move together in the same direction when the force between the two exceeds a predetermined value.

This invention relates to press forming of objects and more particularly it concerns novel arrangements for obtaining controlled embossing of workpieces.

The present invention is particularly useful in connection with the formation of can tops and similar metal objects which are embossed to form tear portions for convenient opening. The beverage industry and other food packaging industries make considerable use of tear open containers. These containers, which are usually of metal, are embossed, or weakened, along lines defining a spiral strip, a contoured segment or some other desired shape. A grasping means is attached to the strip or segment, and when it is pulled or pushed, the container will tear along the emboss lines so that it can be emptied.

A problem has arisen in connection with the extensive use of tear type containers. This problem, which is especially acute where the container is subjected to pressure, concerns the maintenance of proper material thickness in the embossed region. For example, Where aluminum cans are to contain carbonated soft drinks or beer, it is important that the metal thickness remaining along the emboss lines be held to .002 inch plus or minus .00025 inch. If the metal thickness is below these limits the tear out portion is likely to rupture from the internal pressure in the can. If the metal thickness exceeds these limits, the tear out portion will not be cleanly and conveniently removable.

The above described problem is further aggravated by two conditions prevalent in the industry. The first condition is that presently used mass production can forming machines are incapable of holding the desired tolerances without a great number of rejects, and those machines which can hold these tolerances are either too expensive or too slow for mass production needs. The second condition is that commercial grades of can forming sheet aluminum and other sheet metals themselves vary in thickness well over the desired tolerances.

According to the present invention itis possible to mass produce from commercial grade stock metal containers having tear open portions of desired quality. Moreover the present invention permits the adaptation of presently existing machinery to hold the necessary embossing tolerances with a minimum of change and with a minimum of expense. Also machinery modified according to the present invention will operate as fast and, to a certain degree, even more economically than without the invention.

In general, the present invention involves the provision' rice spacer elements are dimensioned to come together and prevent further press shoe closure precisely when the press shoe is close to a point where the embossing ridges on one shoe are displaced from corresponding surfaces of the other shoe by the desired tear line metal thickness. The press is arranged to be actuated such that the press shoes would be brought together more closely than the distance permitted by the spacer elements. The resulting difference in motion is absorbed in a force responsive motion absorption cushion located along the lines `of action of the press actuation elements. This cushion may be, for example, a hydraulic cushion holding one of the press shoes out from its supporting means until subjected to a predetermined force supplied through its spacer elements.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings forming a part of the specification, wherein:

FIG. 1 is a generalized view of the front of a press which may be arranged in accordance with the principles of the present invention;

FIG. 2 is an enlarged fragmentary View showing the die elements of the press of FIG. 1 in opened condition;

FIG. 3 is a view similar to FIG. 2 but showing the die elements in their closed condition;

FIG. 4 is a further enlarged fragmentary view showing the formation by the die elements on the upper and lower shoes of embossing lines on a workpiece;

FIG. 5 is a view showing the embossed portion of the workpiece of FIG. 4 separated from the die elements;

FIG. 6 is a plan view of a can lid having a tear strip formed thereon by the embossing action of the die elements of FIGS. 1-4 inclusive.

As shown in FIG. 1 there is provided a press illustrated generally at 10 into which workpiece sheet material 12 is fed from right to left in a horizontal direction by means of feed rolls 14.

The press 10 is made up of a lower base portion 16, a frame 18, which rises upwardly from the back of the base portion 16, and an upper structure 20, mounted on the frame 18. A lower die shoe 22 is affixed to the base portion 16. An upper die shoe 24 is mounted on the frame 18 to move up and down over the lower die shoe 22 to effect pressing operation. A pair of fixed stripper plates 26 and 28 are provided on one side of the die shoes 22 and 24 to receive the workpiece material 12 and hold it in xed position during the rising of the upper die shoe 24 following each press operation.

An electric drive motor 30 is mounted on the upper structure 20. The drive motor 30 causes a pair of flywheels 32 to turn continuously. These flywheels thus maintain a store of energy which is available for release during press operation. The flywheels 32 are mounted for rotation on a common axle 34 which extends through the upper structure 20. This axle 34 passes through an eccentric housing 36. An eccentric mechanism (not shown) within the housing 36 interconnects the axle 34 with a ram 38 so that the rotary movements of the flywheel will produce up and down movements of the ram. The ram 38 in turn is connected to the upper die shoe 24 and thereby moves the upper die shoe up and down between opened and closed positions. The upper and lower die shoes 24 and 22 are contoured in a cooperative manner such that when they close (i.e., when the upper die shoe 24 moves down), the workpiece sheet material 12 is squeezed and drawn to a corresponding contour.

It will be appreciated that the accuracy or precision of manufacture of the finished workpiece depends, in great part, on the degree to which the upper and lower die shoes come together. That is, the final configuration will depend upon the maintenance of a given minimum clearance between the two die shoes 24 and 22.

Because of the bearings required to support the flywheels 32 and because of the rather massive structures required to support the various movable elements of the press, it becomes exceedingly diflicult to control the press closure clearance to within a few thousandths of an inch. Accordingly, the use of press type devices to perform embossing operations for the forming of tear strips on the finished workpiece has been less than satisfactory.

The press l0, when arranged as illustrated in FIGS. 2 and 3, however, makes it possible to control the embossed thickness of a press formed tear strip to a very high degree of accuracy so that tear strips having predetermined tearing characteristics can be produced very easily.

FIG. 2 shows the configuration of the die elements making up t'ne lower and upper die shoes 22 and 24. As shown in FIG. 2, these die shoes are in their opened condition; that is, the upper die shoe 24 is shown in its uppermost position.

The lower die shoe 22, which is fixed to the base portion 16 of the press 10, has attached thereto an outer shear ring 38. This shear ring is tixedly secured by means of bolts or pins 40 to the lower die shoe 22. The outer shear ring 38 is provided with an upper inside shear corner 44 which is utilized in trimming from the Workpiece sheet material 12 a blank which is then formed into the desired finished configuration.

A central forming die 46 fits closely within the outer shear ring 38. The central forming die 46 has a contoured forming surface 48 which is configured in accordance with the desired finished shape of the article to be formed from the workpiece material 12. The central `forming die 46 additionally is provided with an outer ringshaped horizontal die closure control surface 50 which, as will be seen hereinafter, serves to control the embossed thickness of the finished article.

The central forming die 46 as can be seen in FIG. 2, is movable up and down within the outer shear ring 38. There is provided near the lower portion of the central forming die 46, a protruding shoulder 52. This shoulder fits within a recess 54 formed between the outer shear ring 38 and the upper surface of the lower die shoe 22. Thus the central forming die 46 is movable up and down through a total distance D, defined by the difference in thickness between the shoulder 52 and the recess 54. When the die shoes are in their opened condition, as shown in FIG. 2, the central forming die 46 is in its uppermost position as shown. It is lurged to this position by means of a cushion piston 56 which is ymovable up and down within a bore 58 formed in the lower die shoe 22. The bore 58 communicates via a hydraulic uid inlet passage 60 t0 an external source of continuously applied hydraulic pressure (not shown). When the downward force upon the central forming die 46 exceeds the upward force exerted by the fluid n the piston 56, then the central forming die 46 will move downwardly with the piston displacing hydraulic fluid out through the inlet passage 60. The piston 56 is sealed within the bore 58 by means of a gasket type substance 62 which is squeezed between a pressure plate 64 and the lower surface of the piston S6. The amount of this gasket squeezing can be controlled by means of an adjustable bolt 66 which extends through the pressure plate 64 and is threaded into the piston 56 itself.

The movable upper die shoe 24, which is shown in FIG. 2 in its opened or uppermost position, yhas provided thereon, an outer shear ring 68. This shear ring 68 is xedly secured to the upper die shoe 24 by means of bolts or pins 70. The outer shear ring is formed with a sharp shear corner 74 which is dimensioned to fit closely within the outer shear ring 38 on the lower die shoe 22. This permits the shear corners 74 and 44, on the upper and lower outer shear rings 68 and 38, respectively, to cooperate as the die shoes 22 and 24 are brought together, to shear off a portion of the workpiece material 12 thus forming a blank which is thereafter pressed into its desired finished configuration.

The shear corner 74 formed on the outer shear ring 68 is in part defined by a cooperating die closure control surface 76. This control surface 76 is aligned with and cooperates with the die closure control surface 50 formed on the central forming die 46 of the lower die shoe 22. As will be seen more fully hereinafter, the abutment of the surfaces 76 and 50 establishes the minimum clearance between the forming surfaces on the upper and low-er die elements.

There is additionally provided a central forming die 78 which fits closely within the outer shear ring 68 on the upper die shoe 24. The central forming die 78 is also fixedly attached to the upper die shoe 24 by means of bolts or pins 80. The central forming die 78 is provided with a contoured forming surface 84 which conforms generally to, and cooperates with, the contoured forming surface 48 on the lower central forming die 46. However, the contoured forming surface 84 is additionally provided with various embossing ridges 86 for the formation of a tear strip on the nished pressed article.

Turning now to FIG. 3, it will be seen that as the upper die shoe 24 moves downwardly, the outer shear ring 68 has also moved downwardly so that its shear corner 74 cooperates with the shear corner 44 of the outer shear ring 38 on the lower die shoe 22 to sever from the workpiece material 12, a blank 12a which is thereafter pressed into its nished shape. It will be seen that the shape of the finished workpiece material is controlled by the shape of the cooperating contou-red forming surfaces 48 and 84 on the lower and upper central forming dies 46 and 78, respectively.

As stated previously, the central forming die 46 on the lower die shoe 22 begins operation from its uppermost position as shown in FIG. 2. As the upper die shoe 24 moves downwardly, the central forming die 46 will remain in its uppermost position. It will remain in this position throughout the pressing operation and the formation of the various contours on the workpiece blank 12a. Just as the workpiece blank 12a becomes completely formed however, the die closure control surfaces 50 and 76 on the central forming die 46 and the outer shear ring 68 will abut one another, so that the continued downward force of the upper die shoe 24 bypasses the workpiece blank 12a and is transmitted directly through the outer shear ring 68 to the central forming die 46 causing it to move downwardly against the cushion piston 56. During this downward movement of the lower central forming ring 46, however, the displacement between the contoured forming surfaces 48 and 84 on the two central forming dies 46 and 78 remains constant, this clearance being defined by the relative position of the die closure control surfaces 50 and 76 with respect to the contoured forming surfaces 48 and 84.

It will be noted that the clearance between the upper and lower contoured forming surfaces 84 and 48 is thus 'rendered independent of any variations in total up and down movement of the upper die shoe 24. It will be appreciated of course that these variations must be less than the distance D which corresponds to the total allowable up and down movement of the lower central forming die 46.

It will additionally be noted that there is provided a rather substantial vertical forming groove 88 immediately inside the outer shear ring 68 on the upper die shoe 24. This groove permits the displacement of metal so that at the time the closure control surfaces 50 and 76 close upon each other, the workpiece material will be drawn entirely up into the groove 88 and the closure control surfaces will be able to close directly upon each other.

Turning now to FIGS. 4 and 5, it will be noted that since the minimum displacement between the contoured forming surfaces 48 and 84 is controlled by the die closure control surfaces 50 and 76, there will be established a fixed distance B (FIG. 4) between the tip of the embossing ridges 86 and the corresponding portions of the contoured forming surface 48 on the lower central forming die 46. This distance B also will remain fixed irrespective of the thickness of the workpiece material 12, or of variations in this thickness; assuming, of course, that the maximum thickness of this material never exceeds the total minimum clearance C between the upper and lower forming surfaces 84 and 48. As a consequence, the ridges 86 will form embossed lines 90 as shown in FIG. 5 which detine between them a tear strip 92; the strength of this tearstrip will depend upon the thickness of the material remaining in the embossed regions. Because this thickness, which is the same as the distance B in FIG. 4, is positively established by virtue of the die construction described above and is independent of the thickness or variations thereof in the workpiece material, it is possible to provide tear strip elements having very closely controlled strength characteristics.

FIG. 6 illustrates in plan View, a can lid 94 which may be formed by the above described die arrangement. In such case, as shown, the embossed lines 90 are configured such that the tear strip 92 is in the form of a spiral. A pull tab 96 is attached to one end of the tear strip 92. When the tab 96 is pulled, the lid 94 will tear along the lines 90 as the tear strip 92 is removed in the shape of a spiral ribbon, thus permitting clean and easy removal of the entire lid 94 from the can or container which it closes.

Having thus described the invention with particular reference to the preferred forms thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding the invention, that various other changes and modifications may be made therein without departing from the spirit and scope of the invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. A forming press comprising a pair of press shoes having mutually facing cooperatively contoured surfaces, spacer means arranged in conjunction with said press shoe to limit in a positive manner, the minimum displacement between said contoured surfaces, press actuating means arranged to move said press shoes toward and away from each other, the stroke of said press actuating means being in excess of that necessary to achieve said minimum displacement between said contoured surfaces, and motion absorbing cushion means arranged in series with said press actuating means and said press shoes and operative to absorb the excess stroke of said press actuating means.

2. A forming press as in claim 1 wherein said cushion means comprises a hydraulic piston and cylinder arrangement arranged to support the contoured surface portion of one of said die shoes.

3. A forming press as in claim 1 wherein said spacer means comprises abutment elements on said die shoes.

4. A forming press as in claim 1 wherein said contoured surfaces include ridges which provide controlled embossing of the product formed by said press.

5. A forming press as in claim 3 wherein one of said spacer abutment elements is formed with a shearing corner which cooperates with a corresponding shearing corner on the other press shoe to severl a blank from the workpiece material.

6. A forming press as in claim 5 wherein said abutment elements and said contoured surfaces are displaced in a manner such that said workpiece material is withdrawn from between said abutment elements by the closing action of said contoured surfaces.

7. A forming press as in claim 4 wherein said ridges are congured and arranged to dene a tear strip.

8. A method of embossing sheet material to a precise embossed thickness irrespective of variations in the thickness of said material, said method comprising the steps of supporting said material on one side, moving an embossing tool against said material from the other side and allowing said material to move in the direction of movement of said embossing tool when said embossing tool reaches a predetermined distance from said one side of said material.

9. A method as in claim 8 further including the step of maintaining said predetermined distance at a value less than the thickness of said sheet material.

10. A method as in claim 9 furtherI including the step of forming said material into a desired contour while moving said embossing tool against said material.

References Cited UNITED STATES PATENTS 1,904,920 4/ 1933 Hothersall 72--465 2,985,128 5/1961 Henrickson 72-351 3,333,447 8/ 1967 Alspaugh 72-465 CHARLES W. LANHAM, Primary Examiner. RONALD D. GREFE, Assistant Examiner.

U.S. C1. X.R. 72-456, 465 

